1. Field of the Invention
This invention relates to a color-filter manufacturing method and apparatus for manufacturing a color filter by discharging ink from an ink-jet head on a substrate, thus coloring respective pixels with a plurality of discharge ink, a color filter, a display device, and an apparatus having the display device.
With recent development of personal computers, especially portable personal computers, there is an increasing need for liquid-crystal displays (LCDs), above all, color LCDs. However, for more popularized use of these displays, it is necessary to reduce manufacturing costs of the displays, above all, to reduce manufacturing costs of color filters which take significantly large part of the costs.
Conventionally, various methods have been proposed to meet the above requirements by providing necessary color-filter characteristics, however, none has been established as a solution to satisfy all the necessary characteristics. Known examples of these methods are as follows.
2. Description of Related Art
The most popular first method is a coloring method. This method forms an RGB color filter layer by: (1) applying water-soluble polymer material as coloring material onto a glass substrate; (2) patterning a desired shape by a photolithography process; (3) dipping the obtained pattern into a coloring bath; and (4) repeating the process through steps (1) to (3) thrice.
The second method is a pigment-dispersion method which is replacing the coloring method. This method forms an RGB color filter layer by: (1) forming a photosensitive resin layer where pigment is dispersed on a substrate; (2) patterning a pattern for single color; and (3) repeating the process through steps (1) and (2) thrice.
The third method is an electrodeposition method. This method forms an RGB color filter by: (1) patterning a transparent electrode on a substrate; (2) dipping the substrate on which the transparent electrode has been formed into electrodeposition coating fluid containing pigment, resin, electrolyte and the like to electrodeposit a first color; (3) repeating the process through steps (1) and (2) thrice to obtain an RGB color filter layer; and (4) calcining the color filter.
The fourth method is a printing method. This method forms an RGB color filter by: (1) dispersing, as printing, pigment on thermosetting resin; (2) repeating printing thrice to apply three R, G and B colors; and (3) heat-setting the resin to form colored layer.
Note that any of these methods usually forms a protective layer on the colored layer.
A common problem to these methods is to repeat the same process with respect to three R, G and B colors, which increases costs. In addition, as the number of processes increases, the yield decreases. In the electrodeposition method, as the formable pattern shapes are limited, the technique cannot be applied to manufacture of TFTs. In the printing method, as resolution and smoothness in printing are poor, fine-pitch patterns cannot be formed.
To compensate for these drawbacks, Japanese Patent Application Laid-Open No. 59-75205, Japanese Patent Application Laid-Open No. 63-235901, or Japanese Patent Application Laid-Open No. 1-217320 discloses a method for manufacturing a color filter by using an ink-jet method. This method forms a color filter by discharging R (red), G (green) and B (blue) color ink onto a light-transmitting type substrate, and drying the respective color ink to form a colored pixel portion. The ink-jet method greatly simplifies manufacture process and reduces costs by forming respective RGB pixels at once.
However, in the conventional ink-jet color-filter manufacturing method, the ink is discharged from an ink-jet head in the form of droplets. Accordingly, ink droplets are separated from discharge nozzles at irregular timings, which causes variation in ink-discharge speeds at the respective discharge nozzles. While scanning the ink-jet head, otherwise scanning a stage under a fixed ink-jet head for coloring a color-filter substrate, this variation in ink-discharge speeds might shift ink-arrival positions on the color-filter substrate, thus might cause mixture of colors due to ink-arrival at a neighboring position to a target position, or cause uncolored portion(s) due to omission of coloring a desired pixel.
On the other hand, Japanese Patent Application Laid-Open No. 61-274949 or Japanese Patent Application Laid-Open No. 4-129746 discloses, not discharging ink in the form of ink droplets, but applying ink in the form of pillars before the ink separate from the nozzles of the ink-jet head. As ink in the form of pillars are applied to a coloring object, ink portion unnecessary for actual coloring is drawn back into the nozzles when the ink is separated from the nozzles. This controls the amounts of ink not to exceed necessary amounts, and enables coloring small-diameter dots. Further, since this method does not discharge ink droplets in the air, it is advantageous in the point that only low drive energy is required. Furthermore, as the ink is not separated from the discharge nozzles in the form of droplets, the aforementioned variation in ink-discharge speeds due to shifting of ink-separation timings does not occur.
However, both Japanese Patent Application Laid-Open No. 61-274949 and Japanese Patent Application Laid-Open No. 4-129746 are directed to printing on recording media such as print sheets, but none of them discloses application to manufacture of color-filters.